N̲on-m̲etastatic clone 23, human isoform 1, commonly known as Nm23-H1 is the product of the first identified metastasis suppressor gene NME1. During cancer progression, metastasis becomes prevalent under diminished levels of Nm23-H1. Although Nm23-H1 lacks secretion signal peptide, its presence in the extracellular space is widely reported. Proteomic profiling uncovered Nm23 proteins present inside the extracellular vesicles (EVs) derived from cancer cells. Much evidence suggests that intracellular and extracellular Nm23-H1 exhibit a disparity in their functional significance, whereas the role of vesicular Nm23-H1 remains unknown. Here, we investigated the functional role of vesicular Nm23-H1 by using MDA-MB-231 (highly metastatic, low Nm23-H1) and MCF-7 (low/non-metastatic, high Nm23-H...[ Read more ]

N̲on-m̲etastatic clone 23, human isoform 1, commonly known as Nm23-H1 is the product of the first identified metastasis suppressor gene NME1. During cancer progression, metastasis becomes prevalent under diminished levels of Nm23-H1. Although Nm23-H1 lacks secretion signal peptide, its presence in the extracellular space is widely reported. Proteomic profiling uncovered Nm23 proteins present inside the extracellular vesicles (EVs) derived from cancer cells. Much evidence suggests that intracellular and extracellular Nm23-H1 exhibit a disparity in their functional significance, whereas the role of vesicular Nm23-H1 remains unknown. Here, we investigated the functional role of vesicular Nm23-H1 by using MDA-MB-231 (highly metastatic, low Nm23-H1) and MCF-7 (low/non-metastatic, high Nm23-H1) to mimic breast cancer microenvironment representing highly metastatic and low metastatic cancer cells of the niche, respectively. Our study revealed that Nm23-H1 is indeed encapsulated within exosomes, and its exosomal levels can be manipulated by overexpression and knockdown approaches. Functional assays demonstrated that elevated levels of exosomal Nm23-H1 subdued the ability of MDA-MB-231 derived exosomes to induce migration, suggesting that exosomal Nm23-H1 may act in line with its intracellular metastasis suppressive role. As demonstrated by the transcriptome analysis, exosomes with elevated level of Nm23-H1 caused alterations in the transcript level of multiple cancer-related genes in the recipient cells. Moreover, it stimulated type I interferon signaling via STAT1 phosphorylation. These results indicate an atypical signaling pathway mediated by the uptake of exosomes with elevated level of Nm23-H1, which may account for the anti-metastatic effect of Nm23-H1 in the tumor microenvironment. Additionally, different approaches including luciferase assays and conditioned medium transfer setup were utilized to assess the potential regulation of metastasis suppressor proteins by virtue of microRNAs (miRNAs) encapsulated in MDA-MB-231 exosomes. However, the attempts were met with limited success. This study further demonstrates that overexpression of Nm23-H1 can apparently regulate exosome biogenesis pathway, altering the amount of multiple other encapsulated proteins that may subsequently affect the function of breast cancer cell-derived exosomes. These findings illustrate an anti-migratory role of Nm23-H1 via exosomes which may facilitate the development of anti-metastasis therapies against breast cancer and potentially extend to other cancer types.